2 
BULLETIN OF THE BUREAU OF FISHERIES 
paper the two deep places nearest to the biological station were selected. One of them, 
which will be designated as Station A, is but a quarter of a mile away, and the other 
one, Station B, is about a mile from headquarters. Station A differs from the other 
stations in being partially sheltered by a high wooded bluff from the full force of 
the frequent, strong, northwest winds, while Station B is in a position to get the 
maximum effect of such winds. The thermocline at Station B was ordinarily 
several feet deeper than that of Station A. 
The general plan of operations included the submergence of a series of wire 
cages attached at different levels to a rope which was suspended from a wooden 
buoy or float. The float was anchored in the desired situation, and the rope to 
which the cages were attached had a weight fastened to its lower end to keep the 
rope taut and maintain a constant depth for the cages. The cages were made 
of galvanized wire netting of about 3/2-iiich mesh and were cubical in form, with 
each surface 1 foot square. Fish of several kinds were placed in each of the cages, 
and they were let down to the desired depths, where they remained until the next 
visit. Temperature readings and tests for the oxygen content and the hydrogen-ion 
condition at approximately the same levels as those at which the cages were placed 
made a part of the records. Subsequent visits at varying intervals of time were 
made for the purpose of examination of the condition of the caged fish, the removal 
of dead ones, and the addition of others. Not infrequently additional chemical and 
temperature examinations were made for comparison with the former ones. 
For hearty cooperation in the provision of equipment and in the securing of nec- 
essary assistance thanks are due Dr. G. R. La Rue, the director of the biological station. 
Dr. P. S. Welch generously made the few chemical tests that were necessary the 
hrst season. In 1921 Dr. Minna Jewell, who was a member of the station corps 
of assistants, rendered most valuable service in making all of the chemical determi- 
nations and records. For this work she was particularly well fitted because of 
much previous experience in such chemical studies on this lake and elsewhere. 
During the first season the observations were of a preliminary sort for the 
purpose of finding o\it whether the limiting depth is very definite, and whether 
the fish that were obtained in shallow water were suitable for the tests at greater 
depths. The results seemed to show that the lower limit of the body of water, 
which had the conditions necessary for sustaining the life of fish, was very sharply 
defined, and also made it apparent that the fish from shallow water were suitable 
for the tests. 
The first test was made July 26, 1920, at Station A. Data of Doctor Welch, 
taken three days earlier, showed a thermocline between 45 and 53 feet, with plenty 
of oxygen at 45 feet. Two specimens of Lepomis gibhosus were placed in each of 
three minnow pails at depths of 40, 55, and 65 feet at 4.30 p. m. At 6.45 p. m. of 
the same day in each of the pails at the two lower levels one fish was dead and the 
other one nearly dead. Those in the pail at 40 feet were in good condition and were 
still living 24 hours later. 
On July 28 at 10.40 a. m. yearling bullheads and suckers were placed in the 
pails at the same depths as before, and at 7 p. m. those in the two lower pails were 
dead, while those in the upper one were in good condition, and most of the latter 
were still living 24 hours later. 
